ZHANG Cai-mei, ZHANG Qi-hang, ZHANG Lu, CHENG Yang-pei (BATF Industry Co., Ltd., Foshan 528322, Guangdong, China)
Abstract: In this experiment, vinyl acetate was added to the traditional styrene-acrylic emulsion, which reduced the production cost of traditional styrene-acrylic emulsion while preserving the performance advantages of traditional styrene-acrylic emulsion. In the experiment, the amount of inner core was taken and the reaction temperature was explored. It was found that when the amount of inner core was 10%, TBHP and Vc were used as redox initiator and the reaction temperature was 70 ℃, the reaction for four hours could get better reaction results. The core∶middle layer∶shell ratio of 40∶10∶50 in the case of better shell get good economic benefits, reducing the costs by 12.1%.
In recent years, increasing real estate development projects The pressure on environmental protection is increasing day by day, and the amount of construction emulsion is rising. Because of its environmental friendliness, aqueous emulsions have received more and more attention and applications. Among them, styrene-acrylic emulsions are favored by many customers for their excellent film toughness, water resistance, scrub resistance and alkali resistance, and lower prices. However, as the price of styrene continues to rise, its terminal prices have also risen. This directly led to a sudden increase in production costs of downstream manufacturers, and they urgently needed a product with similar performance to the current styrene-acrylic emulsion but with a lower price.
Acetate-acrylic emulsion (copolymerization of vinyl acetate and butyl acrylate) can replace the existing styrene-acrylic emulsion to a certain extent, and at the same time has an absolute price advantage, so it has always maintained a large share in the low-end emulsion market. However, due to its hydrophilic nature, vinyl acetate emulsions have inherent defects in water resistance. This also directly caused the acetic acid emulsion to lose the capital to compete in the high-end market.
1 Experimental mechanism
Ethylene vinyl acetate (VAc) and styrene (St) were simultaneously put into a reactor for emulsion polymerization. Due to the large difference in reactivity ratios (r1 = 55, r2 = 0.01), good polymers could not be obtained. . And it has the following reactions during copolymerization:
～ VAc · + VAc → ～ VAcVAc · k11 = 3 700 L / (mol · s)
～ VAc · + St → ～ VAcSt · k12 = 370 000 L / (mol · s)
～ St · + VAc → ～ StVAc · k21 = 3.2 L / (mol · s)
It can be seen from this that St will greatly hinder the homopolymerization of Vac, and the combination of these factors directly leads to extremely difficult direct polymerization of Vac and St.
2 Experimental design ideas
Although direct polymerization of Vac and St is very difficult, both Vac and BA (n-butyl acrylate) and St and BA can copolymerize well. The graft reaction between polymers is beneficial to the formation of the core-shell structure. Therefore, it is very important to use polymer chemistry to cleverly design the particles without changing the composition of the raw materials and increasing the cost. The core-shell structure of the intermediate transition layer solves the above problems.
According to the emulsion polymerization mechanism, combining the characteristics of vinyl acetate and styrene, it was decided to adopt a three-layer core-shell structure to solve the problem that Vac and St cannot be directly copolymerized.
In order to show the excellent performance of the styrene-acrylic emulsion, the solution uses Vac homopolymerization and nucleation, the middle layer is wrapped with BA, and the outermost layer is wrapped with styrene-acrylic emulsion. The reason for using the Vac core is mainly to reduce the cost of the emulsion while also having certain performance; the middle layer is wrapped with BA, which can not only consume the remaining Vac but also provide convenience when the shell is wrapped, preventing the shell St monomer from invading the core and causing the core The shell is flipped; the outermost styrene-acrylic emulsion provides excellent performance and prevents moisture from penetrating the core.
In this experiment, the preparation of the core part is the key to the success of the next two steps. The particle size of the core part directly affects the thickness of the subsequent coating layer and the overall particle size. The addition of the core part is also the cost of this solution. The key to decline. The seed emulsion polymerization method can be used to make the system have better stability and narrower particle size distribution, so the core preparation will be carried out by the seed emulsion polymerization process.
In the preparation of the nuclear part, since the Vac has a boiling point of 71.8 ° C, the thermal initiator efficiency is low at this temperature, so this scheme uses a redox initiator system. Around 70 ℃, the reaction rate of both the redox system and the thermally initiated system is relatively slow, so the reaction time is set to 4 h. At the same time, it is considered to increase the reaction temperature to 88 ℃ after adding the middle layer to wrap, so that the subsequent styrene-acrylic emulsion layer (shell layer) can be carried out at a faster reaction rate, and the effect of process differences on the performance of the shell emulsion can be reduced.
The significance of this method is that the cost of the emulsion is reduced by using vinyl acetate, so as to achieve the performance similar to that of the existing styrene-acrylic emulsion while adding part of the vinyl acetate to reduce the cost of raw materials.
3 Experimental part
3.1 Raw materials and instruments (see Tables 1 and 2)
3.2 Polymerization process A
three-layer core-shell process seed polymerization method was used to synthesize the emulsion.
3.2.1 Core layer
188.8.131.52 Reference formula for the preparation of the core layer emulsion (see Table 3)
184.108.40.206 Preparation of the core layer emulsion
In a four-necked flask, add 3 g of polyvinyl alcohol and 400 g of deionized water at 90 ° C After dissolving, it was put into a heating device and held at 70 ° C. 15 g of sodium dodecylbenzenesulfonate, 300 g of deionized water, 990 g of vinyl acetate, 10 g of methacrylic acid, and 0.15 g of t-butyl hydroperoxide were prepared into a pre-emulsion and kept stirring for 15 min. After the stirring is completed, 10% of the pre-emulsion is added to the bottom of the kettle, and at the same time, an aqueous solution of 0.15 g of t-butyl hydroperoxide and 20 g of deionized water and an aqueous solution of 0.15 g of FF-6 and 30 g of deionized water are added. After incubation for 0.5 h, the remaining pre-emulsion was started to drip, and an aqueous solution of 0.15 g of FF-6 and 100 g of deionized water was added to the initiator at the same time. The drip time was 4 h, and then a post-treatment procedure was performed. Post-treatment lowered the temperature to 65 ° C using 0.3 g of tert-butyl hydroperoxide and 30 g of deionized water in an aqueous solution and 0.3 g of FF-6 and 30 g of deionized water in an aqueous redox reaction. The dropping time was 30 min. Finally, the kettle was kept for 15 minutes.
3.2.2 Intermediate layer
220.127.116.11 Reference formula for the preparation of intermediate layer emulsion (see Table 4)
Note: The final solid content of the emulsion in the table is 53.3% ± 0.5%.
18.104.22.168 Preparation of intermediate layer emulsion
800 g of the core layer emulsion prepared in the previous step was added to the bottom of the kettle, and the temperature was raised to 70 ° C. 1.5 g of sodium dodecylbenzenesulfonate, 60 g of deionized water, 99 g of n-butyl acrylate, 1 g of acrylic acid, and 0.15 g of t-butyl hydroperoxide were prepared into a pre-emulsion, and slowly added to the bottom of the kettle At the same time, an aqueous solution of 0.15 g of FF-6 initiator and 20 g of deionized water was dropped into the initiator at the same time, and the dropping time was about 1 h. After the dropwise addition was completed, the temperature was raised to 88 ° C and the shell layer was added in the next step.
22.214.171.124 Reference formula for the preparation of shell emulsion (see Table 5)
126.96.36.199 Preparation of the shell emulsion
3.5 g sodium dodecylbenzenesulfonate, 559 g deionized water, 319 g styrene , 208 g of n-butyl acrylate, and 5.3 g of acrylic acid were made into a shell pre-emulsion for later use. An aqueous solution of 1.2 g of potassium persulfate and 40 g of deionized water was used as the shell initiator. After the middle layer reaction is completed and enters the heating stage, the reaction kettle is held for 30 minutes. After the completion of the heat preservation, pour 6.2 g of the shell layer initiator into the reactor as the initial introduction of the shell layer reaction, and put it into the bottom of the kettle at one time to maintain the reaction temperature of 88 ℃. Then, the shell pre-emulsion and the remaining initiator were added dropwise, and the pre-emulsion drop time was 70 min.
After the dropwise addition was completed, the temperature was maintained at 88 ° C for 30 minutes, and then the temperature was lowered to 68 ° C for post-treatment. The post-treatment uses an aqueous solution of 0.6 g of tert-butyl hydrogen peroxide and 10 g of deionized water, and an aqueous solution of 0.3 g of Vc and 20 g of deionized water, and is added dropwise at the same time. And finally cool out of the kettle.
4 Results and discussion
The purpose of this solution is to reduce the current price of styrene-acrylic emulsions, which are constantly rising, so cost control is the primary goal.
According to the cost calculation in Tables 6 to 8, it can be seen that when the quality of the core accounts for 50%, the cost can be saved by 15.0%. Combined with the thickness and cost accounting table of the styrene-acrylic emulsion wrapped on the outer wall after nucleation, the experiment selected a scheme with a core mass of 40 kg, an intermediate layer mass of 10 kg, and a shell mass of 50 kg. Compared with the cost of styrene-acrylic emulsion, the cost at this time was reduced by about 12.1%.
4.2 Effect of reaction temperature on the polymerization of vinyl acetate
This project focuses on the preparation of the core layer. As the internal filling material of the core layer, Vac has a boiling point of 71.8 ° C, so the corresponding reaction temperature was explored (theoretical solid content: 48.78%). The results are shown in Table 9.
According to Table 9, it can be seen that the reaction rate is faster as the temperature increases, but since the boiling point of vinyl acetate is 71.8 ° C, as the temperature increases, especially after reaching 80 ° C, the solid content of the emulsion obtained by polymerization The obvious decrease and the sharp increase in particle size indicate that there is a large number of explosions and Vac evaporation at the same time, which is a very dangerous situation and also caused a lot of waste of resources. At a temperature of 65 ℃, even the redox system is quite inefficient, there are a lot of monomers in the emulsion, and the smell is quite pungent. Based on Table 9, it is determined that the reaction temperature of the nuclear system is preferably 70 ° C.
4.3 Effect of seeding amount on the polymerization of vinyl acetate
According to Table 10, it can be found that as the seeding amount increases, the particle size of the emulsion seed continues to decrease, but as the reaction drops, the polymerization reaction of 15% of seeding appears Extremely abnormal particle size explosion. This is because a large amount of heat released during the polymerization of vinyl acetate caused the local temperature to be too high, localized explosion polymerization, and a relatively serious agglomeration phenomenon. Although the narrowest particle size distribution was obtained with a 5% seed volume, the final particle size was close to 132.5 nm, which was not conducive to the subsequent two packages. Therefore, a 10% seed volume was considered as a whole.
4.4 Effect of reaction temperature on the polymerization of vinyl acetate The
optimal conditions were selected to make nuclear seeds, and the results obtained after two wrappings are shown in Table 11.
It can be seen from the results in Table 11 that this solution can pass the GB / T 20623-2006 “Emulsion for Architectural Coatings” national standard test and meet the general requirements for use of architectural emulsions. The typical characteristics of this solution are compared with the styrene-acrylic emulsion and ethyl acetate emulsion of the same polymerization process, and the formula is shown in Table 12.
According to the national standard GB / T 9756-2018 “Synthetic Resin Emulsion Interior Wall Coatings”, the scrub resistance comparison between the self-made vinyl acetate-styrene emulsion and the styrene-acrylic emulsion and vinegar-acrylic emulsion is shown in Table 13.
Note: (1) Test the upper and lower parts of the board on the same board. The upper part is marked as 1 and the lower part is marked as 2. The purpose is to avoid the uneven surface of the board, the level of the instrument or the brush. The error caused by the problem.
(2) The comparison samples are all self-made vinyl acetate-styrene emulsions, and the test samples correspond to the styrene-acrylic emulsion in the second column and the acetonitrile emulsion in the third column in order.
(3) Scrub resistance ratio = [(test sample 1 + test sample 2) ÷ 2] ÷ [(comparative sample 1 + comparative sample 2) ÷ 2] × 100%, the formula reflects the degree of deviation between the test sample and the comparative sample.
By comparing Table 13, it can be seen that the scrub resistance of the self-made vinyl acetate-styrene emulsion is similar to that of the styrene-acrylic emulsion, while the scrub resistance of the vinegar-acrylic emulsion is much worse than that of the self-made vinyl acetate-styrene emulsion. Therefore, the self-made vinyl acetate-styrene emulsion can replace the styrene-acrylic emulsion for interior wall paint, thereby achieving the purpose of reducing costs.
This solution uses vinyl acetate as the core of a commercially available traditional styrene-acrylic emulsion, which has dropped by about 12.1% compared to the original emulsion. At the same time, it uses mature styrene-acrylic emulsion products as the shell, which overcomes the poor water resistance of ordinary vinegar-acrylic emulsion . A feasible route for the acetic acid benzene emulsion was found. In this solution, the boiling point during the polymerization of vinyl acetate and the compatibility with styrene were fully taken into account. Specific evasion measures were taken and good results were obtained.
Exploration and found a better synthetic formula and process: Acetic acid m (core): m (middle layer): m (shell) is 40:10:50, the acetic acid and acrylic core uses 10% seeding technology, and reacts at 70 ℃ for 4 h ; The middle layer was added dropwise for 1 h; the shell layer was added dropwise for 70 min. A low-cost emulsion conforming to the national standard can be prepared and compared with the styrene-acrylic emulsion / vinegar-acrylic emulsion. According to the scrub resistance results, it is shown that the self-made vinyl acetate-styrene emulsion can replace the styrene-acrylic emulsion for interior wall paint.